A method of ink-jet printing is known which comprises placing an information carrier opposite jets filled with an expendable liquid printing material, and generating pressure pulses in those jets for feeding the printing material by portions onto the information carrier (U.S. Pat. No. 4,580,148, class 346/140R). In the known method a pressure pulse is created in the jets due to pulse heating of the liquid printing material which results in the formation of steam in the heating zone, rapid expansion of the liquid and the expulsion of droplets of the liquid from the jet.
A disadvantage of this method is that a source of thermal action on the liquid printing material is placed directly in each jet and is controlled from outside, which makes realization of this method difficult when there are a large number of jets. Furthermore, this method does not make it possible to obtain a high frequency of expulsion of droplets, since before the generation of a subsequent pressure pulse it is necessary to reduce the temperature in the jet for the flow therein of the next portion of liquid printing material.
An inkjet printing head realized according to the patent cited above comprises the same number of resistors for heating the liquid material as there are jets therein. Each resistor has a lead for connecting it to a voltage source. In order to expel droplets from one or another jet, the power supply circuit of a corresponding resistor is closed. When a current pulse flows through that resistor, it is heated, the liquid substance in the zone in which the resistor is positioned is heated to a steam state, as a result of which the liquid, expanding, creates an impact pulse expelling a droplet through the jet. Then, after the liquid has cooled, the described process can be repeated.
A disadvantage of such heads is their structural complexity, since the number of resistors should correspond to the number of jets mounted with a small spacing therebetween and provided with a system of current leads; low resolution since the aforesaid jets with resistors cannot be positioned with a small spacing; low reliability, since the mode of multiple pulse heating of resistors to a sufficiently high temperature predetermines their limited service life; low productivity since the next expulsion of droplets from a jet is only possible after the temperature therein has been reduced and there is a flow therein of the next portion of expendable liquid printing material.